The present invention relates to a process for manufacturing mineral wool by fiberizing a molten mineral composition, using tools made of a cobalt-based alloy having a high-temperature mechanical strength in an oxidizing medium, such as molten glass, and to cobalt-based alloys that can be used at high temperature, especially for the production of articles for the manufacture and/or hot-conversion of glass or other mineral material, such as components of machines for manufacturing mineral wool.
One fiberizing technique, called internal centrifuging, consists in letting liquid glass drop continuously into an assembly of parts rotating at a very high rotation speed about their vertical axis. A master part, called a “spinner dish”, receives the glass against one of its walls called the “band” which is pierced with holes through which the glass passes due to the effect of the centrifugal force in order to escape therefrom on all sides in the form of molten filaments. An annular burner located above the outside of the spinner dish, which produces a downward blast of gas hugging the outer wall of the band, deflects these filaments downwards and attenuates them. The latter then “solidify” in the form of glass wool.
The spinner dish is a fiberizing tool which is highly stressed thermally (heat shocks when stopping and starting and the creation, in steady use, of a temperature gradient along the part), mechanically (centrifugal force, and erosion due to the passage of the glass) and chemically (oxidation and corrosion by the molten glass, and by the hot gasses expelled by the burner around the spinner dish). Its main modes of deterioration are: deformation of the vertical walls by hot creep, horizontal or vertical cracking, or wear of the fiberizing orifices by erosion, which purely and simply require the components to be replaced. Their constituent material must therefore withstand the above for a production time long enough to remain compatible with the technical and economic constraints of the process. For this purpose, materials are sought which exhibit a certain ductility, creep strength and corrosion and/or oxidation resistance.
A conventional material for producing these tools is a superalloy based on nickel and chromium, reinforced by chromium and tungsten carbides, which can be used up to a maximum temperature of about 1000 to 1050° C.
To fiberize glasses at a higher temperature, especially for manufacturing mineral wool from highly viscous glasses such as basalt, it has been proposed to use superalloys based on cobalt, this being a refractory element (melting point equal to 1495° C.) which gives the matrix of the alloy a higher high-temperature intrinsic mechanical strength than a nickel-based matrix.
These alloys always contain chromium for oxidation resistance, and generally carbon and tungsten in order to obtain a reinforcing effect caused by the precipitation of carbides. They also contain nickel in solid solution, the nickel stabilizing the face-centred cubic crystal lattice of cobalt at all temperatures.
Thus, WO-A-99/16919 discloses a cobalt-based alloy having improved high-temperature mechanical properties, essentially comprising the following elements (in percentages by weight of the alloy):
Cr 26 to 34%Ni  6 to 12%W  4 to 8%Ta  2 to 4%C0.2 to 0.5%Feless than 3%Siless than 1%Mnless than 0.5%Zrless than 0.1%,the balance consisting of cobalt and inevitable impurities, the molar ratio of tantalum with respect to carbon being of the order of 0.4 to 1.
The selection of carbon and tantalum proportions is intended to form, in the alloy, a dense but discontinuous network of intergranular carbides essentially consisting of chromium carbides in the Cr7C3 and (Cr,W)23C6 forms and of tantalum carbides TaC. This selection gives the alloy improved high-temperature mechanical properties and oxidation resistance, allowing a molten glass at a temperature of 1080° C. to be fiberized.